Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ]
  1 /*
  2  *  binfmt_misc.c
  3  *
  4  *  Copyright (C) 1997 Richard G√ľnther
  5  *
  6  *  binfmt_misc detects binaries via a magic or filename extension and invokes
  7  *  a specified wrapper. This should obsolete binfmt_java, binfmt_em86 and
  8  *  binfmt_mz.
  9  *
 10  *  1997-04-25 first version
 11  *  [...]
 12  *  1997-05-19 cleanup
 13  *  1997-06-26 hpa: pass the real filename rather than argv[0]
 14  *  1997-06-30 minor cleanup
 15  *  1997-08-09 removed extension stripping, locking cleanup
 16  *  2001-02-28 AV: rewritten into something that resembles C. Original didn't.
 17  */
 18 
 19 #include <linux/module.h>
 20 #include <linux/init.h>
 21 #include <linux/sched.h>
 22 #include <linux/binfmts.h>
 23 #include <linux/slab.h>
 24 #include <linux/ctype.h>
 25 #include <linux/file.h>
 26 #include <linux/pagemap.h>
 27 #include <linux/namei.h>
 28 #include <linux/mount.h>
 29 #include <linux/syscalls.h>
 30 
 31 #include <asm/uaccess.h>
 32 
 33 enum {
 34         VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
 35 };
 36 
 37 static LIST_HEAD(entries);
 38 static int enabled = 1;
 39 
 40 enum {Enabled, Magic};
 41 #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
 42 #define MISC_FMT_OPEN_BINARY (1<<30)
 43 #define MISC_FMT_CREDENTIALS (1<<29)
 44 
 45 typedef struct {
 46         struct list_head list;
 47         unsigned long flags;            /* type, status, etc. */
 48         int offset;                     /* offset of magic */
 49         int size;                       /* size of magic/mask */
 50         char *magic;                    /* magic or filename extension */
 51         char *mask;                     /* mask, NULL for exact match */
 52         char *interpreter;              /* filename of interpreter */
 53         char *name;
 54         struct dentry *dentry;
 55 } Node;
 56 
 57 static DEFINE_RWLOCK(entries_lock);
 58 static struct file_system_type bm_fs_type;
 59 static struct vfsmount *bm_mnt;
 60 static int entry_count;
 61 
 62 /* 
 63  * Check if we support the binfmt
 64  * if we do, return the node, else NULL
 65  * locking is done in load_misc_binary
 66  */
 67 static Node *check_file(struct linux_binprm *bprm)
 68 {
 69         char *p = strrchr(bprm->interp, '.');
 70         struct list_head *l;
 71 
 72         list_for_each(l, &entries) {
 73                 Node *e = list_entry(l, Node, list);
 74                 char *s;
 75                 int j;
 76 
 77                 if (!test_bit(Enabled, &e->flags))
 78                         continue;
 79 
 80                 if (!test_bit(Magic, &e->flags)) {
 81                         if (p && !strcmp(e->magic, p + 1))
 82                                 return e;
 83                         continue;
 84                 }
 85 
 86                 s = bprm->buf + e->offset;
 87                 if (e->mask) {
 88                         for (j = 0; j < e->size; j++)
 89                                 if ((*s++ ^ e->magic[j]) & e->mask[j])
 90                                         break;
 91                 } else {
 92                         for (j = 0; j < e->size; j++)
 93                                 if ((*s++ ^ e->magic[j]))
 94                                         break;
 95                 }
 96                 if (j == e->size)
 97                         return e;
 98         }
 99         return NULL;
100 }
101 
102 /*
103  * the loader itself
104  */
105 static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
106 {
107         Node *fmt;
108         struct file * interp_file = NULL;
109         char iname[BINPRM_BUF_SIZE];
110         char *iname_addr = iname;
111         int retval;
112         int fd_binary = -1;
113         struct files_struct *files = NULL;
114 
115         retval = -ENOEXEC;
116         if (!enabled)
117                 goto _ret;
118 
119         /* to keep locking time low, we copy the interpreter string */
120         read_lock(&entries_lock);
121         fmt = check_file(bprm);
122         if (fmt)
123                 strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
124         read_unlock(&entries_lock);
125         if (!fmt)
126                 goto _ret;
127 
128         if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
129                 retval = remove_arg_zero(bprm);
130                 if (retval)
131                         goto _ret;
132         }
133 
134         if (fmt->flags & MISC_FMT_OPEN_BINARY) {
135 
136                 files = current->files;
137                 retval = unshare_files();
138                 if (retval < 0)
139                         goto _ret;
140                 if (files == current->files) {
141                         put_files_struct(files);
142                         files = NULL;
143                 }
144                 /* if the binary should be opened on behalf of the
145                  * interpreter than keep it open and assign descriptor
146                  * to it */
147                 fd_binary = get_unused_fd();
148                 if (fd_binary < 0) {
149                         retval = fd_binary;
150                         goto _unshare;
151                 }
152                 fd_install(fd_binary, bprm->file);
153 
154                 /* if the binary is not readable than enforce mm->dumpable=0
155                    regardless of the interpreter's permissions */
156                 if (file_permission(bprm->file, MAY_READ))
157                         bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
158 
159                 allow_write_access(bprm->file);
160                 bprm->file = NULL;
161 
162                 /* mark the bprm that fd should be passed to interp */
163                 bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
164                 bprm->interp_data = fd_binary;
165 
166         } else {
167                 allow_write_access(bprm->file);
168                 fput(bprm->file);
169                 bprm->file = NULL;
170         }
171         /* make argv[1] be the path to the binary */
172         retval = copy_strings_kernel (1, &bprm->interp, bprm);
173         if (retval < 0)
174                 goto _error;
175         bprm->argc++;
176 
177         /* add the interp as argv[0] */
178         retval = copy_strings_kernel (1, &iname_addr, bprm);
179         if (retval < 0)
180                 goto _error;
181         bprm->argc ++;
182 
183         bprm->interp = iname;   /* for binfmt_script */
184 
185         interp_file = open_exec (iname);
186         retval = PTR_ERR (interp_file);
187         if (IS_ERR (interp_file))
188                 goto _error;
189 
190         bprm->file = interp_file;
191         if (fmt->flags & MISC_FMT_CREDENTIALS) {
192                 /*
193                  * No need to call prepare_binprm(), it's already been
194                  * done.  bprm->buf is stale, update from interp_file.
195                  */
196                 memset(bprm->buf, 0, BINPRM_BUF_SIZE);
197                 retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
198         } else
199                 retval = prepare_binprm (bprm);
200 
201         if (retval < 0)
202                 goto _error;
203 
204         retval = search_binary_handler (bprm, regs);
205         if (retval < 0)
206                 goto _error;
207 
208         if (files) {
209                 put_files_struct(files);
210                 files = NULL;
211         }
212 _ret:
213         return retval;
214 _error:
215         if (fd_binary > 0)
216                 sys_close(fd_binary);
217         bprm->interp_flags = 0;
218         bprm->interp_data = 0;
219 _unshare:
220         if (files)
221                 reset_files_struct(current, files);
222         goto _ret;
223 }
224 
225 /* Command parsers */
226 
227 /*
228  * parses and copies one argument enclosed in del from *sp to *dp,
229  * recognising the \x special.
230  * returns pointer to the copied argument or NULL in case of an
231  * error (and sets err) or null argument length.
232  */
233 static char *scanarg(char *s, char del)
234 {
235         char c;
236 
237         while ((c = *s++) != del) {
238                 if (c == '\\' && *s == 'x') {
239                         s++;
240                         if (!isxdigit(*s++))
241                                 return NULL;
242                         if (!isxdigit(*s++))
243                                 return NULL;
244                 }
245         }
246         return s;
247 }
248 
249 static int unquote(char *from)
250 {
251         char c = 0, *s = from, *p = from;
252 
253         while ((c = *s++) != '\0') {
254                 if (c == '\\' && *s == 'x') {
255                         s++;
256                         c = toupper(*s++);
257                         *p = (c - (isdigit(c) ? '' : 'A' - 10)) << 4;
258                         c = toupper(*s++);
259                         *p++ |= c - (isdigit(c) ? '' : 'A' - 10);
260                         continue;
261                 }
262                 *p++ = c;
263         }
264         return p - from;
265 }
266 
267 static char * check_special_flags (char * sfs, Node * e)
268 {
269         char * p = sfs;
270         int cont = 1;
271 
272         /* special flags */
273         while (cont) {
274                 switch (*p) {
275                         case 'P':
276                                 p++;
277                                 e->flags |= MISC_FMT_PRESERVE_ARGV0;
278                                 break;
279                         case 'O':
280                                 p++;
281                                 e->flags |= MISC_FMT_OPEN_BINARY;
282                                 break;
283                         case 'C':
284                                 p++;
285                                 /* this flags also implies the
286                                    open-binary flag */
287                                 e->flags |= (MISC_FMT_CREDENTIALS |
288                                                 MISC_FMT_OPEN_BINARY);
289                                 break;
290                         default:
291                                 cont = 0;
292                 }
293         }
294 
295         return p;
296 }
297 /*
298  * This registers a new binary format, it recognises the syntax
299  * ':name:type:offset:magic:mask:interpreter:flags'
300  * where the ':' is the IFS, that can be chosen with the first char
301  */
302 static Node *create_entry(const char __user *buffer, size_t count)
303 {
304         Node *e;
305         int memsize, err;
306         char *buf, *p;
307         char del;
308 
309         /* some sanity checks */
310         err = -EINVAL;
311         if ((count < 11) || (count > 256))
312                 goto out;
313 
314         err = -ENOMEM;
315         memsize = sizeof(Node) + count + 8;
316         e = kmalloc(memsize, GFP_USER);
317         if (!e)
318                 goto out;
319 
320         p = buf = (char *)e + sizeof(Node);
321 
322         memset(e, 0, sizeof(Node));
323         if (copy_from_user(buf, buffer, count))
324                 goto Efault;
325 
326         del = *p++;     /* delimeter */
327 
328         memset(buf+count, del, 8);
329 
330         e->name = p;
331         p = strchr(p, del);
332         if (!p)
333                 goto Einval;
334         *p++ = '\0';
335         if (!e->name[0] ||
336             !strcmp(e->name, ".") ||
337             !strcmp(e->name, "..") ||
338             strchr(e->name, '/'))
339                 goto Einval;
340         switch (*p++) {
341                 case 'E': e->flags = 1<<Enabled; break;
342                 case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
343                 default: goto Einval;
344         }
345         if (*p++ != del)
346                 goto Einval;
347         if (test_bit(Magic, &e->flags)) {
348                 char *s = strchr(p, del);
349                 if (!s)
350                         goto Einval;
351                 *s++ = '\0';
352                 e->offset = simple_strtoul(p, &p, 10);
353                 if (*p++)
354                         goto Einval;
355                 e->magic = p;
356                 p = scanarg(p, del);
357                 if (!p)
358                         goto Einval;
359                 p[-1] = '\0';
360                 if (!e->magic[0])
361                         goto Einval;
362                 e->mask = p;
363                 p = scanarg(p, del);
364                 if (!p)
365                         goto Einval;
366                 p[-1] = '\0';
367                 if (!e->mask[0])
368                         e->mask = NULL;
369                 e->size = unquote(e->magic);
370                 if (e->mask && unquote(e->mask) != e->size)
371                         goto Einval;
372                 if (e->size + e->offset > BINPRM_BUF_SIZE)
373                         goto Einval;
374         } else {
375                 p = strchr(p, del);
376                 if (!p)
377                         goto Einval;
378                 *p++ = '\0';
379                 e->magic = p;
380                 p = strchr(p, del);
381                 if (!p)
382                         goto Einval;
383                 *p++ = '\0';
384                 if (!e->magic[0] || strchr(e->magic, '/'))
385                         goto Einval;
386                 p = strchr(p, del);
387                 if (!p)
388                         goto Einval;
389                 *p++ = '\0';
390         }
391         e->interpreter = p;
392         p = strchr(p, del);
393         if (!p)
394                 goto Einval;
395         *p++ = '\0';
396         if (!e->interpreter[0])
397                 goto Einval;
398 
399 
400         p = check_special_flags (p, e);
401 
402         if (*p == '\n')
403                 p++;
404         if (p != buf + count)
405                 goto Einval;
406         return e;
407 
408 out:
409         return ERR_PTR(err);
410 
411 Efault:
412         kfree(e);
413         return ERR_PTR(-EFAULT);
414 Einval:
415         kfree(e);
416         return ERR_PTR(-EINVAL);
417 }
418 
419 /*
420  * Set status of entry/binfmt_misc:
421  * '1' enables, '' disables and '-1' clears entry/binfmt_misc
422  */
423 static int parse_command(const char __user *buffer, size_t count)
424 {
425         char s[4];
426 
427         if (!count)
428                 return 0;
429         if (count > 3)
430                 return -EINVAL;
431         if (copy_from_user(s, buffer, count))
432                 return -EFAULT;
433         if (s[count-1] == '\n')
434                 count--;
435         if (count == 1 && s[0] == '')
436                 return 1;
437         if (count == 1 && s[0] == '1')
438                 return 2;
439         if (count == 2 && s[0] == '-' && s[1] == '1')
440                 return 3;
441         return -EINVAL;
442 }
443 
444 /* generic stuff */
445 
446 static void entry_status(Node *e, char *page)
447 {
448         char *dp;
449         char *status = "disabled";
450         const char * flags = "flags: ";
451 
452         if (test_bit(Enabled, &e->flags))
453                 status = "enabled";
454 
455         if (!VERBOSE_STATUS) {
456                 sprintf(page, "%s\n", status);
457                 return;
458         }
459 
460         sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
461         dp = page + strlen(page);
462 
463         /* print the special flags */
464         sprintf (dp, "%s", flags);
465         dp += strlen (flags);
466         if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
467                 *dp ++ = 'P';
468         }
469         if (e->flags & MISC_FMT_OPEN_BINARY) {
470                 *dp ++ = 'O';
471         }
472         if (e->flags & MISC_FMT_CREDENTIALS) {
473                 *dp ++ = 'C';
474         }
475         *dp ++ = '\n';
476 
477 
478         if (!test_bit(Magic, &e->flags)) {
479                 sprintf(dp, "extension .%s\n", e->magic);
480         } else {
481                 int i;
482 
483                 sprintf(dp, "offset %i\nmagic ", e->offset);
484                 dp = page + strlen(page);
485                 for (i = 0; i < e->size; i++) {
486                         sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
487                         dp += 2;
488                 }
489                 if (e->mask) {
490                         sprintf(dp, "\nmask ");
491                         dp += 6;
492                         for (i = 0; i < e->size; i++) {
493                                 sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
494                                 dp += 2;
495                         }
496                 }
497                 *dp++ = '\n';
498                 *dp = '\0';
499         }
500 }
501 
502 static struct inode *bm_get_inode(struct super_block *sb, int mode)
503 {
504         struct inode * inode = new_inode(sb);
505 
506         if (inode) {
507                 inode->i_mode = mode;
508                 inode->i_uid = 0;
509                 inode->i_gid = 0;
510                 inode->i_blocks = 0;
511                 inode->i_atime = inode->i_mtime = inode->i_ctime =
512                         current_fs_time(inode->i_sb);
513         }
514         return inode;
515 }
516 
517 static void bm_clear_inode(struct inode *inode)
518 {
519         kfree(inode->i_private);
520 }
521 
522 static void kill_node(Node *e)
523 {
524         struct dentry *dentry;
525 
526         write_lock(&entries_lock);
527         dentry = e->dentry;
528         if (dentry) {
529                 list_del_init(&e->list);
530                 e->dentry = NULL;
531         }
532         write_unlock(&entries_lock);
533 
534         if (dentry) {
535                 dentry->d_inode->i_nlink--;
536                 d_drop(dentry);
537                 dput(dentry);
538                 simple_release_fs(&bm_mnt, &entry_count);
539         }
540 }
541 
542 /* /<entry> */
543 
544 static ssize_t
545 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
546 {
547         Node *e = file->f_path.dentry->d_inode->i_private;
548         loff_t pos = *ppos;
549         ssize_t res;
550         char *page;
551         int len;
552 
553         if (!(page = (char*) __get_free_page(GFP_KERNEL)))
554                 return -ENOMEM;
555 
556         entry_status(e, page);
557         len = strlen(page);
558 
559         res = -EINVAL;
560         if (pos < 0)
561                 goto out;
562         res = 0;
563         if (pos >= len)
564                 goto out;
565         if (len < pos + nbytes)
566                 nbytes = len - pos;
567         res = -EFAULT;
568         if (copy_to_user(buf, page + pos, nbytes))
569                 goto out;
570         *ppos = pos + nbytes;
571         res = nbytes;
572 out:
573         free_page((unsigned long) page);
574         return res;
575 }
576 
577 static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
578                                 size_t count, loff_t *ppos)
579 {
580         struct dentry *root;
581         Node *e = file->f_path.dentry->d_inode->i_private;
582         int res = parse_command(buffer, count);
583 
584         switch (res) {
585                 case 1: clear_bit(Enabled, &e->flags);
586                         break;
587                 case 2: set_bit(Enabled, &e->flags);
588                         break;
589                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
590                         mutex_lock(&root->d_inode->i_mutex);
591 
592                         kill_node(e);
593 
594                         mutex_unlock(&root->d_inode->i_mutex);
595                         dput(root);
596                         break;
597                 default: return res;
598         }
599         return count;
600 }
601 
602 static const struct file_operations bm_entry_operations = {
603         .read           = bm_entry_read,
604         .write          = bm_entry_write,
605 };
606 
607 /* /register */
608 
609 static ssize_t bm_register_write(struct file *file, const char __user *buffer,
610                                size_t count, loff_t *ppos)
611 {
612         Node *e;
613         struct inode *inode;
614         struct dentry *root, *dentry;
615         struct super_block *sb = file->f_path.mnt->mnt_sb;
616         int err = 0;
617 
618         e = create_entry(buffer, count);
619 
620         if (IS_ERR(e))
621                 return PTR_ERR(e);
622 
623         root = dget(sb->s_root);
624         mutex_lock(&root->d_inode->i_mutex);
625         dentry = lookup_one_len(e->name, root, strlen(e->name));
626         err = PTR_ERR(dentry);
627         if (IS_ERR(dentry))
628                 goto out;
629 
630         err = -EEXIST;
631         if (dentry->d_inode)
632                 goto out2;
633 
634         inode = bm_get_inode(sb, S_IFREG | 0644);
635 
636         err = -ENOMEM;
637         if (!inode)
638                 goto out2;
639 
640         err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
641         if (err) {
642                 iput(inode);
643                 inode = NULL;
644                 goto out2;
645         }
646 
647         e->dentry = dget(dentry);
648         inode->i_private = e;
649         inode->i_fop = &bm_entry_operations;
650 
651         d_instantiate(dentry, inode);
652         write_lock(&entries_lock);
653         list_add(&e->list, &entries);
654         write_unlock(&entries_lock);
655 
656         err = 0;
657 out2:
658         dput(dentry);
659 out:
660         mutex_unlock(&root->d_inode->i_mutex);
661         dput(root);
662 
663         if (err) {
664                 kfree(e);
665                 return -EINVAL;
666         }
667         return count;
668 }
669 
670 static const struct file_operations bm_register_operations = {
671         .write          = bm_register_write,
672 };
673 
674 /* /status */
675 
676 static ssize_t
677 bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
678 {
679         char *s = enabled ? "enabled" : "disabled";
680 
681         return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
682 }
683 
684 static ssize_t bm_status_write(struct file * file, const char __user * buffer,
685                 size_t count, loff_t *ppos)
686 {
687         int res = parse_command(buffer, count);
688         struct dentry *root;
689 
690         switch (res) {
691                 case 1: enabled = 0; break;
692                 case 2: enabled = 1; break;
693                 case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
694                         mutex_lock(&root->d_inode->i_mutex);
695 
696                         while (!list_empty(&entries))
697                                 kill_node(list_entry(entries.next, Node, list));
698 
699                         mutex_unlock(&root->d_inode->i_mutex);
700                         dput(root);
701                 default: return res;
702         }
703         return count;
704 }
705 
706 static const struct file_operations bm_status_operations = {
707         .read           = bm_status_read,
708         .write          = bm_status_write,
709 };
710 
711 /* Superblock handling */
712 
713 static const struct super_operations s_ops = {
714         .statfs         = simple_statfs,
715         .clear_inode    = bm_clear_inode,
716 };
717 
718 static int bm_fill_super(struct super_block * sb, void * data, int silent)
719 {
720         static struct tree_descr bm_files[] = {
721                 [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
722                 [3] = {"register", &bm_register_operations, S_IWUSR},
723                 /* last one */ {""}
724         };
725         int err = simple_fill_super(sb, 0x42494e4d, bm_files);
726         if (!err)
727                 sb->s_op = &s_ops;
728         return err;
729 }
730 
731 static int bm_get_sb(struct file_system_type *fs_type,
732         int flags, const char *dev_name, void *data, struct vfsmount *mnt)
733 {
734         return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
735 }
736 
737 static struct linux_binfmt misc_format = {
738         .module = THIS_MODULE,
739         .load_binary = load_misc_binary,
740 };
741 
742 static struct file_system_type bm_fs_type = {
743         .owner          = THIS_MODULE,
744         .name           = "binfmt_misc",
745         .get_sb         = bm_get_sb,
746         .kill_sb        = kill_litter_super,
747 };
748 
749 static int __init init_misc_binfmt(void)
750 {
751         int err = register_filesystem(&bm_fs_type);
752         if (!err) {
753                 err = register_binfmt(&misc_format);
754                 if (err)
755                         unregister_filesystem(&bm_fs_type);
756         }
757         return err;
758 }
759 
760 static void __exit exit_misc_binfmt(void)
761 {
762         unregister_binfmt(&misc_format);
763         unregister_filesystem(&bm_fs_type);
764 }
765 
766 core_initcall(init_misc_binfmt);
767 module_exit(exit_misc_binfmt);
768 MODULE_LICENSE("GPL");
769 
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